The present invention relates to catalysts useful in the oxidation and/or ammoxidation of olefins. More specifically, the present invention relates to a novel process for producing oxidation and/or ammoxidation catalysts having superior properties.
It is well known that olefins can be oxidized to oxygenated hydrocarbons such as unsaturated aldehydes and acids, for example, acrolein and methacrolein, and acrylic and methacrylic acids. It is also well known that olefins can be ammoxidized to unsaturated nitriles such as acrylonitrile and methacrylonitrile. The value of such oxygenated hydrocarbons and unsaturated nitriles is generally well recognized with acrylonitrile being among the most valuable monomers available to the polymer industry for producing useful polymeric products.
Various catalytic processes are known for the oxidation and/or ammoxidation of olefins. Such processes commonly react an olefin or an olefin-ammonia mixture with oxygen in the vapor phase in the presence of a catalyst. For the production of acrolein and acrylonitrile, propylene is the generally used olefin reactant and for the production of methacrolein and methacrylonitrile, isobutylene is the generally used olefin reactant.
Many different catalysts have been disclosed as useful in the oxidation and ammoxidation of olefins. For example, see U.S. Pat. Nos. 3,882,159 and 3,746,657. Also see commonly assigned application Ser. No. 748,609, filed Dec. 7, 1976, the disclosure of which is incorporated herein by reference. As will be noted, catalysts based on bismuth and molybdenum, i.e. bismuth molybdate catalysts, promoted with various additional elements such as iron, cobalt, nickel, potassium, phosphorus, chromium, manganese and the like show special utility for these reactions.
Bismuth molybdate catalyst have been prepared in the past by a number of different techniques. For example, Example III of U.S. Pat. No. 3,746,657 shows a preparation method comprising forming a mixture of potassium hydroxide, ammonium molybdate and silica, adding to the mixture phosphoric acid, solutions in nitric acid of the nitrates of cobalt, iron, nickel and bismuth, and more silica to form a slurry, then spray drying and calcining to form the catalyst. Application Ser. No. 748,609 discloses a catalyst preparation technique in which an aqueous solution of cobalt nitrate and nickel nitrate, an aqueous solution of potassium nitrate and iron nitrate, an aqueous nitric acid solution of bismuth nitrate and a silica sol are added in order to an aqueous solution of ammonium heptamolybdate and phosphoric acid, and the composition so obtained sprayed dried and calcined to form the catalyst. This application discloses another catalyst proparation technique in which an aqueous nitric acid solution of ferric nitrate and bismuth nitrate is added to a previously formed aqueous slurry containing ammonium heptamolybdate, phosphoric acid, arsenic acid, silica sol, nickel nitrate and cobalt nitrate, the composition so obtained heated until a gel forms, and the gel dried and calcined to produce the ultimate catalyst.
Each of the known techniques of catalyst preparation has relative advantages and disadvantages. Also, there has been some indication that the catalytic properties of the ultimate catalysts produced can be improved if specific catalysts preparation techniques are followed. As yet, however, there is no known catalyst preparation technique which is both simple and easy to perform and capable of enhancing the catalytic properties of the ultimate catalyst.
Accordingly, it is an object of the present invention to provide a catalyst preparation technique especially suited for preparing bismuth molybdate type catalysts which is both simple and easy to perform as well as capable of enhancing the catalytic properties of the catalyst produced.